This invention relates to a support apparatus for workpieces while advancing along a reheat furnace; and more particularly, to such an apparatus having an upper and at least one, but preferably two, lower cord members interconnected by tubular web members, all of which are water-cooled and form triangular open spaces for the passage of heat radiation to the underside faces of workpieces to eliminate or at least minimize skid marks.
As is known in the art, water-cooled skids or beams are used to support metallic workpieces in a furnace during heating to a desired temperature. Workpieces, such as billets, blooms or slabs, can be heated to a desired temperature for processing in a rolling mill in a continuous pusher-type furnace or in a walking-beam type furnace. In a pusher-type furnace, a cold workpiece is transported to the charging end where pushers are operated to advance the workpiece against a continuous stream of workpieces into the furnace. When a cold workpiece is advanced into the furnace, a heated workpiece passes through a discharge door at the opposite end of the furnace. In a walking-beam type furnace, workpieces are advanced in the furnace chamber with step-by-step movements by walking-beam assemblies that form stationary and movable supports for the workpieces. The movable supports first lift the workpiece from the stationary support. The movable support is then advanced toward the exit end of the furnace through a predetermined distance, lowered onto the stationary supports. Thereafter, the movable support is retracted for the next cycle of operation. One form of construction of the movable and stationary supports for a walking-beam type furnace can be found in my U.S. Pat. No. 4,290,752.
In a pusher-type furnace and, to a lesser extent, in a walking-beam type furnace, variations to the elevated temperature of the workpiece occur at the site where the workpiece is in contact with a support member while exposed to the high-temperature environment in the furnace. In a continuous slab reheat furnace, for example, the slabs are progressively advanced forwardly toward the discharge end of the furnace on water-cooled skids. Burners are located above and below the skid level and furnish heat by radiation and convection to both the top and bottom surfaces of the slabs while the slabs reside in the heating zones and, depending upon the furnace construction, a preheating zone. The water-cooled skids normally terminate at the entrance to a soaking zone where the slabs are supported on a continuous refractory hearth. In the soaking zone, only top burners are provided since the slabs arrive at the soaking zone at approximately the desired rolling temperature.
In the soaking zone, principle heat requirements for the slab are met. In this zone, skid marks which are visible and essentially are cooler, strip-like areas extending across the slabs due to contact with the water-cooled skids, must be eliminated, if possible, as well as other temperature non-uniformities while maintaining the desired furnace temperature to compensate for radiation losses. However, it has been found that even after a slab is treated in the soaking zone, there still remains a temperature differential between the sites of the skid marks and the remaining part of the slab. Direct radiation heating of the skid mark sites is not possible because the face surface of the slab containing the skid marks is in continuous contact with the hearth.
As is known in the art, water-cooled skid pipes for a pusher-type reheat furnace generally take the form of spaced-apart and generally parallel pipes extending in the direction of slab movement. The skid pipes are anchored at the charging end of the furnace and terminate at a furnace wall where the pipes are connected to water supply lines. Wear bars are welded or otherwise secured to the top surface of the skid pipes. The skid pipes are usually provided with a covering of heat insulating-material. Extending transversely to the water-cooled skid pipes are other pipes which are supported by the walls of the furnace as well as, in some instances, by downwardly-extending props which are also pipes. The transversely-arranged pipes are spaced apart at intervals so as to provide sufficient support for the length of the water-cooled skid pipes. The transversely-arranged support pipes are also provided with outer coverings of heat-insulating material and they are continuously fed with a water for cooling. Various forms of water-cooled skid pipes are shown, for example, in U.S. Pat. Nos. 2,482,878; 3,236,507; 3,311,357; 3,345,050; 3,706,448; 3,804,584 and 4,056,351.
Conventional well-known skid pipes drain substantial amounts of heat from the furnace due to the requirement for a continuous flow of cooling water in the skid pipes as well as the transversely-extending pipes on which the skid pipes are supported. The skid pipes are relatively large, for example, the pipe may have a five-inch outside diameter with a one-inch wall thickness on which an outer layer of heat insulation is applied, whereby the resulting skid structure necessarily immediately adjacent the undersurface of the slab, masks a large area of the slab from heat radiation. In other words, the ultimate size of the water-cooled skid pipe structure is sufficiently large and in close proximity to the downwardly-directed surfaces of the slab so that not only is the actual area of contact between the skid pipe and the slab obscured from impingement with heat radiation but also presents a poor radiant shaped factor that isolates or shadows areas immediately adjacent either side of the skid rail from heat radiation. The size of the skid pipe is selected, of course, to withstand loading imposed by the workpieces. The loading of the skid pipe includes not only the weight of the workpieces but also large stresses occurring transversely to the extended length of the skid pipes due to expansion of the workpieces during the heating process. Transverse loading of the skid pipes is a significant factor that must be dealt with in pusher-type furnaces. In walking-beam type heating furnaces, transverse loading of the workpiece-support member occurs to a lesser extent because the workpieces are intermittently contacted by the walking-beam mechanism.